U.S. Pat. No. 6,975,949 describes a digital printer having a full-width array scanning spectrophotometer. A spectrophotometer is a device that measures fine gradations in color of light reflected from a target surface; these fine measurements can be used to calibrate or otherwise control a digital color printer, by examining images produced by the printer. A “full-width array” indicates that at least a large portion of the width across the paper output path is examined, such as by one or more long linear arrays of photosensors, so that a large portion of a printed image is effectively tested by the spectrophotometer.
As mentioned in the '949 patent, a full-width array scanning spectrophotometer is readily adapted from such an array used in image input, such as for a digital color copier. Being able to sample color outputs from across the full width of a sheet being output is useful from the standpoint of checking for certain types of image quality phenomena. For instance, if the marking technology used by the printer involves an ink-jet printhead or an LED bar, deficiencies in a portion of the printhead or bar will be manifest only in a portion of the resulting printed image; being able to survey the full width of the output print sheet is therefore valuable in isolating print defects.
In a high-speed, production context, it is known to provide detectors and image sensors immediately downstream of a printing apparatus for various purposes, as shown in U.S. Pat. Nos. 5,488,458; 6,324,353; and 6,684,035.